PHP 4.2.2 for vBulletin 3.8.9

I know PHP 4.2.2 and vBulletin 3.8.x is OLD and am aware of the risks of using them, so please spare me the warnings. - I am trying to install ntPHPSelector so I can set a specific domain to use PHP 4.2.2 whereas the rest of the WHM accounts can use the most recent/stable PHP version.

I can't find where to switch or set a specific account to use PHP 4.2.2 as it's not listed. Could someone guide me on how to do this please?